The present invention relates to a semiconductor device, and more particularly relates to a semiconductor device that uses a redundant power supply, for example.
A semiconductor device such as a system LSI (Large Scale Integrated circuit) executes a stop sequence for safely stopping the whole of a system including the semiconductor device under control of a control circuit, in a case where an abnormality, such as voltage drop, occurs in an output voltage of a power supply.
However, if an output voltage of a regular power supply that supplies a power-supply voltage to the control circuit becomes abnormal and the power-supply voltage cannot be supplied from the regular power supply to the control circuit, the control circuit cannot execute the stop sequence, so that an analog circuit inside the semiconductor device may be damaged, for example. In addition, if the power-supply voltage cannot be supplied from the regular power supply to the control circuit, it is likely that an unintended signal is transmitted from the control circuit to the inside or outside of the semiconductor device, leading to a malfunction of the system, for example.
Therefore, a technique for supplying the power-supply voltage to the control circuit stably has been proposed. According to Japanese Unexamined Patent Application Publication No. 2009-055686, for example, at least one spare power supply is provided in addition to a currently used power supply, and an output voltage of the currently used power supply is monitored. When the output voltage of the currently used power supply drops to a threshold value or lower, an operation for starting up the spare power supply that is stopping is performed and, on condition that start-up of the spare power supply is completed, a power-supply switching operation that makes the spare power supply a new currently used power supply is performed.